This invention relates to apparatus for use in applying tension to lengths of pipe, for example, for testing the tensile strength of joints of pipe used in oil well and like drill strings.
It is well known in the oil industry to test a joint of pipe for strength (or to straighten a pipe length) in a machine which is adapted to apply axial tension to the pipe. A machine of this nature commonly includes elongated beams or the like with hydraulic cylinders at one end. A joint of pipe to be tested is gripped at its opposite ends by gripping assemblies associated with the beams and the hydraulic cylinders respectively so that extension of the cylinders applies axial tension to the pipe.
The forces employed in machines of the above type are considerable, so that should a pipe be defective and rupture under load, the sudden release of tension may cause one or both ends of the pipe to be forcibly expelled from the machine with dangerous consequences. The forces involved can, for example, be of a magnitude to propel part of a ruptured pipe as much as 200 feet.
The present invention provides apparatus for the application of tensile stress to a pipe which includes means for precluding expulsion of a portion of the pipe (and the associated fittings) in the event of a pipe failure resulting in rupture of the pipe during the application of tensile stress thereto.